CA1072669A - Packaging system for cooling electronic equipment - Google Patents

Abstract

PACKAGING SYSTEM FOR COOLING ELECTRONIC EQUIPMENT

Abstract of the Disclosure Electrical circuit boards are aligned with corresponding slots in a plenum chamber. Each slot has an outwardly turned lip.
The chamber has a cross section which decreases uniformly from a blower. Further electrical components are placed in the path of inlet air to the blower. All of these units are rigidly mounted on a swing-out gate.

Description

Background of the Invention The present invention concerns cooling for electrical appara-tus, and is particularly directed toward arrangements for air-cooling electronics equipment hav;ng components densely mounted on printed-circuit boards or the like.
As electronics components decrease in size ~or a given amount of function, and as packaging density increases, the ultimate limita-tion on overall size is the amount of heat which can be dissipated.
It has always been easier to miniaturize electronics components than to miniaturize their cooling.
-- Another problem concerns maintaining adequate cooling when the cooling load, e.g., the number and position of printed-circuit boards in a package, is variable. In the embodiment to be des-cribed, some circuit boards represent optional features which are not present on every machine. A related problem occurs upon ser-vicing of the machine. In most electronics assemblies, the com-; ponents must be moved for servicing or inspection. But, in many cases, this involves moving the components relat;ve to the cooling system such that adequate heat removal cannot be maintalned while the boards are accessible.
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1 Summary of the Invention The present invention provides adequate cooling for an assem-bly of densely packaged circuit boards or cards even when some of the cards are removed from the assembly; that is, when the cooling load is not constant. The invention further provides full cooling when the circuit boards are in a position where they are easily accessible for servicing. Moreover, cooling systems accord-ing to invention are physically small and are easy and inexpensive to manufacture.
Broadly speaking, the invention includes a blower for supply-ing cooling air to a plenum chamber having a decreasing cross section away from the blower. On a wall adjacent the circuit boards to be cooled, the chamber has a series of slots. Each slot is provided with an out-turned lip lying outside the chamber and adjacent one of the circuit boards. The blower, plenum chamber and circuit-board assembly are mounted together rigidly in a hinged frame which can be opened as a unit for servicing and inspection.
Drawings FIG. 1 is a simplified top rear perspective view of a gate assembly for holding and cooling an electronics package, incor-porating an embodiment of the invention.
FIG. 2 is a top plan view of an electronics apparatus in-corporating the gate of FIG. 1.
Detailed_Description In the simplified perspective view of FIG. 1, numeral 100 denotes generally a gate member molded in a single piece of ~ ;
structural foamed plastic. An L-shaped rear bay 110 has an up-standing wall 111 and a solid floor 112 having molded lugs 113 for fastening a power-supply module (not shown in FIG. 1) R09-75-022 ~2-~7~

1 Blower means 120, also ;ntegrally molded in gate 100, con-tains an enclosed houslng 121 o~ a conventional "scroll" design for a squirrel-cage blower rotor 122. Rotor 122 is driven by a motor (not shown) mounted on the bottom surface 123 of housing 120. Inlet aperture 124 is surrounded by upstanding walls 125, 1269 and 111. A plenum chamber 130 is partially defined by walls 137 and 138 forming an L-shaped projection 131 molded in gate 100 and communicating with housing 120.
Chamber 130 is covered by a stamped metal sheet 132 having a front wall 135 containing a series of slots 133 and outturned lips 134, and having mounting flange 135' fastened to wall 138. (The bottom wall 139 of sheet 132, which is fastened to wall 137, is shown in FIG. 2). In the illustrative embodiment shown, the lips and slots are generally trapezoidal, having bases of 4.6 and 4.1 cm., and a width of 0.8 cm. The slot-to-slot spacing is about 1.6 cm. The rectangular cross section of plenum chamber 130, as defined by projection 131 and sheet 132, decreases un;~ormly in area from its entrance 135 to its forward end 136. This decrease in area is preferably achieved entirely by decreasing the width between sheet 132 and side wall 137 of projection 131, while the height between upper and lo~er walls 138 remains constant. Sheet 132 is slightly shorter than the length of chamber 130, to pro-vide a final air exit at 137.
Finally, gate 120 includes an integrally molded support means defining a front bay 140. Wall 141 is attached at one end to ;
end 136 of plenum chamber 130 and to bar 142, shown broken away for clarity. Wall 143 has one end attached to wall 141; its other end is attached to wall 111. The upper surfaces of wall 141 and bar 142, along with ledges formed in walls 143 and '''.

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'72669 111, form a mounting surface 1~4 for a backplane (not shown) containing sockets for a number of circuit boards.
FIG. 2 is a top plan view of a desktop data processor 200 including the gate 100 shown in FIG. 1. Since gate 100 is in its "open" position in FIG. 2, it is seen from the bottom, i.e., upside down with respect to FIG. 1.
FIG. 2 shows a simplified outline of a power-supply module 150 mounted in rear bay 110. Broadly speaking, module 150 com-prises a number of component packages, such as 151-154, mounted on a support board 155. Board 155 is in turn fastened to lugs 113, FIG. 1. A solid metal safety cover 114 is attached to the side and bottom of wall 111, as it appears in FIG. 2. Cover 114 is also fastened to the left end of wall 112 and to walls 125 and 126.
FIG. 2 also shows an electronics assembly 160 mounted in front bay 140. Backplane 161 is a stiff horizontal board mounted on surface 144, FIG. 1. It contains a number of parallel edge-connector sockets such as 162 into which circuit boards such as 163 may be inserted in a conventional manner. In this illustrative embodiment, boards 163 are printed-circuit boards each holding many components and modules. Backplane 161 merely provides physi-cal support ancl electrical isolation for sockets 162, inter-socket electrical connections are provided by wires wrapped on posts (not shown) on each socket to the rear of backplane 161 as seen in FIG. 2, and/or by printed-circuit wiring (not shown) on backplane 161. Sockets 162 are disposed paral1el to each other and are aligned with respective ones of the lips 134 on plenum-chamber sheet 132, such that circuit boards 163 are coplanar with lips 134 but separated therefrom by a small distance, e.g., less than about 1.5 cm. The height of plenum chamber 130 (i.e., in the direction out of the plane of FIG. 2) is less than half the height of boards 163.

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`1 Gate 100 is attached to a structural foamed-plastic lower housing 210 of processor 100 by hinge means 220. A conventional "invisible" hinge 221 is fastened between arms 222 molded in gate 100 and vertical posts 223 molded into lower housing 210. Another hinge 224 is fastened between posts 225 in gate 100 and posts 226 in housing 210. This arrangement allows gate 100 to swing up to 180 about a horizontal axis, from the position shown in FIG. 2 to a "closed" position in which gate 100 lies fully within lower housing 210. In the closed position, metal brackets 101 and 102 may be screwed to upstanding posts 211 and 212 molded in housing 210. The upper edges of circuit boards 163 rest against a resilient foam-rubber cushion 213 on a raised platform 214 molded into the bottom of housing 110.
In this way, gate 100 and its cooling system and electronics `
components are rigidly secured within housing 110 in the closed position. At the same time, the inter-board wiring on backplane 161 is easily accessible for servicing from above. Then, when gate 100 is opened and laid flat on the same surface upon which housing 110 rests, the power supply 150 and the individual cir-Z0 cuit boards 163 are immediately accessible. Processor 100 may continue to operate indefinitely in the open position, since full cooling is retained.
Lower housing 110 also holds other electronics modules, shown in outline form to illustrate their spatial relationship to gate 100. Keyboard 220 is positioned ahead of a slightly sloping vertical panel 230. Magnetic-tape unit 240 and cathode-ray tube (CRT) display 250 abut panel 130. Control bracket 260 is for use by service ~`
personnel, and is accessible in both the open and closed positions of gate 100. When gate 100 is closed, a louvered upper housing (not shown) may be fitted over lower housing 210 to the .:

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1 rear o~ panel 230.
In operation, squirrel-cage blower rotor 122 draws inlet cool-ing air from the rear of bay 110 into blower housing 120. This re-latively high-volume low-velocity air flows across power supply 150 to cool components 151 - 154 before being drawn into blower housing 120. Rotor 122, which projects slightly beyond the plane of wall 132 as shown in FIG. 2, then propels the air into plenum chamber 130, preferably at a lineal velocity of about 15 meters per second in the present embod;ment. The air then proceeds through slots 134 and between circuit boards 163 in bay 160.
The combination of the uniformly decreasing cross section of plenum chamber 130, the uniformly spaced slots 133 and the perpen-dicular out-turned lips 134 produces a stream of cooling air of sub-stantially constant volume from slot to slot along the length of wall 132 and flowing perpendicularly thereto. These characteristics are substantially.independent of the cooling load, that is, inde-pendent of the number of circuit boards 163 actually present in bay 140. Each slot 133 presents a higher airflow impedance than that of -the space between two adjacent boards 163. Lips 134, although ~hey lie wholly outside of chamber 120, are effective to deflect the air-flow through a complete right angle, whether or not a circuit board is inserted in the corresponding socket 162. For the aforementioned air velocity of 15 m/sec., this directional change is best accom-plished when each lip 134 is downstream from its associated slot 133.
At higher velocities such.as about 30 m/sec., however, the lips are more effective when positioned at the upstream sides of the slots.
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1 The cooling air exiting slots 133 has a high normal velocity component. Very little bac~splash occurs when the lips and boards are less than about 1.5 cm. apart. Therefore, the areas above and below boards 163 need not be sealed in order to maintain pro-per air flow. Moreover, adequate cooling is achieved even though the vertical height of boards 163 is much greater than that of lips 134. Lips 134 in -turn need not be taller or wider than slots 133 and do not extend into chamber 13n~ so that these lips may be easily Fabricated by merely bending out the interiors of the slots.
These characteristics also result in a small size For the entire cooling system, in relation to the si~e of the cooling load.
Another advantage of the embodiment shown in FIGS. 1 and 2 is that the cooling air is drawn into and exhausted from pro-cessor 200 at relatively large distances from blower rotor 122. - -This configuration reduces blower noise sufficiently that other acoustic absorption materials are unnecessary.

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Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A packaging system for cooling electrical apparatus mounted on a plurality of parallel circuit boards, said system comprising:
a single, integrally formed gate structure having a blower housing provided with an inlet aperture, a plurality of walls partially defining a plenum chamber communicating with said blower housing, and support means defining a bay for holding said electrical apparatus;
means rigidly mounted to said blower housing For propelling cooling air from said inlet aperture to said plenum chamber; and a sheet rigidly attached to said plenum chamber so as to im-part a uniformly decreasing interior cross section to said plenum chamber, said sheet being provided with a plurality of slots and a corresponding plurality of out-turned lips extending wholly out-side said plenum chamber and substantially parallel to said cir-cuit boards.

2. The sytem of Claim 1, wherein said gate means includes a plurality of further walls defining a second bay for holding fur-ther electrical apparatus, said second bay communicating with said blower housing such that said cooling air is passed across said further apparatus before being drawn into said inlet aperture.

3. The system of Claim 1, further comprising:
a lower housing for supporting said gate in a closed position;
and hinge means attached to said lower housing and to said gate so as to permit said gate to be rotated through about 180° to an open position.

4. A system for providing cooling air to a plurality of parallel circuit boards, said system comprising:
blower means having a housing provided with an inlet aper-ture, and having means for propelling said cooling air; and a plenum chamber communicating with said blower housing and having a plurality of walls defining a substantially uniformly decreasing width and a substantially constant height, one of said walls having a plurality of slots and a like plurality of out-turned lips adjacent said slots, said lips being disposed wholly outside said plenum chamber and extending toward said circuit boards so as to provide a substantially constant supply of said cooling air to each of said circuit boards regardless of the num-ber of said boards.

5. The system of Claim 4, wherein said lips extend perpendicularly from said one wall and are substantially coplanar with but separated from said circuit boards.

6. The system of Claim 5, wherein said lips are disposed on the downstream edges of said slots.

7. The system of Claim 6, wherein said air-propelling means pro-vides said cooling air to said plenum chamber at a lineal velocity of at least about 15 meters per second.

8. The system of Claim 4, wherein the height of said lips is not greater than about one-half the height of said circuit boards.

9. The system of Claim 4, further comprising a second plurality of walls defining a rear bay for holding additional electrical apparatus, said rear bay for holding additional electrical appara-tus, said rear bay communicating with said blower housing via said inlet aperture such that said cooling air is drawn through said rear bay before entering said inlet aperture.